Most people planning a European trip default to the same shortlist: Paris, Rome, Barcelona, maybe Amsterdam. What they miss is the pocket of Europe sitting quietly between all of those better-known names — a four-country stretch where the history is deeper, the food is more interesting, and the crowds are noticeably thinner. Belgium, France, the Netherlands, and Luxembourg together cover less ground than most US states. But the density of what's packed into that space — medie